This investigation is designed to increase our understanding of the linked development of family and peer relationships from early to mid-adolescence as these in turn predict adaptive and maladaptive psychosocial functioning. Family and peer relationships are conceptualized in terms of adolescents' progress in the developmental tasks of establishing autonomy in social relationships while maintaining and developing attachment and affiliative bonds. An intensive, longitudinal, observation, and multi-reporter design is used to pursue three conceptually-bounded studies. Study 1: Normative Development of Peer Relationships, assesses development over time in autonomy and attached affiliative processes in peer relationships, considering linkages between these two processes. Study 2: Family Interactions as Predictors of Peer Relationships, considers ways in which autonomy and attachment processes in adolescent-parent interactions set the stage for the emergence of similar processes (e.g., resistance to peer pressure and formation of supportive friendships) in developing peer relationships. Study 3: Sequelae of Developing Peer Relationships, considers ways in which important aspects of adolescent psychosocial functioning (e.g., depressive symptoms, externalizing behavior problems, changing relationships with parents, and sexual risk-taking) can be understood as outcomes of developing peer relations. This investigation will address these questions using intensive, observational and multi- reporter data from a socio-demographically heterogeneous sample of 172 families with early adolescents, along with three peers of these adolescents who will be assessed in for waves spaced annually. Assessments will included attachment interviews, and observation and interview sessions with parents, adolescents, and peers. Important socio-demographic factors that may influence the development of peer relationships are also incorporated into models as appropriate. This investigation is designed to yield information that can inform: (a) remedial and preventative psychosocial interventions targeting peer influences; (b) efforts to assess social functioning in adolescence; and (c) efforts to understand the development of critical social relationships across the lifespan as these are linked to psychosocial functioning.